1. Field of the Invention
This invention relates to electronically driven video displays for displaying computer, television or other informational or entertainment images or text which displays can have flexible shape enabling novel displays according to the invention to be curved, rolled, flexed or folded. The inventive displays can be embodied in a wide variety of forms, including high definition television monitors, laptop and desktop computer monitors, cell phone displays, sports stadium displays, highway signs and the like, in conventional configurations, and also in novel, variable form configurations. The invention also relates to the manufacture of such displays.
2. Description of Related Art
Including Information Disclosed under 37 CFR 1.97 and 37 CFR 1.98
In the emerging information age, at the beginning of the twenty-first century, video display panels are commonplace household and office items appearing in many forms. Brilliant full-color screens radiate real time or recorded action images from large areas of home theater walls, of Times Square buildings and from sports stadia scoreboards. Compact-monochrome panels communicate important daily trivia from phones, cars, ovens and other appliances. And few businessmen, scientists or teachers can properly practice their professions without the ubiquitous personal computer and its accompanying display. Nor is a home considered complete without one, or more likely, several television monitors. As the burgeoning Internet drives an exponential growth in communications, and as intelligent devices proliferate, video display panels will emerge into ever more market niches.
Surprisingly, prior to this invention, the display device is, all too often, a bulky, heavy, resource-hungry, energy-consuming cathode ray tube. Though alternative technologies proliferate, they either lack picture quality or are more expensive, limiting their fields of use. There has accordingly long been a need for compact, low resource, energy efficient display panels.
A drawback of conventional displays known to the present inventors is that they have a fixed form, typically comprising a rigid rectangular display panel which provides the viewed display area. The extent of the desired display area thus sets a minimum size parameter on devices incorporating the display panel, the rigidity and geometric permanence of which requires the display panel geometry to be maintained from the factory to the user and for the life of the device. Given the appeal of large screen video displays, and for other reasons, it would be desirable to have flexible or shapable displays capable of adopting a form more compact than their displayed extent when not in use. For example, it would be especially attractive to provide a portable computer display that could be rolled, curved or even folded into a more compact form than conventional laptop computers, which typically have a footprint of about 30 cm (12 in) by about 23 cm (9 in).
There is accordingly a need for a display technology which can adapt to emerging market needs, can solve the problem of providing a flexible video display, or display panel, capable of conforming to more than one useful geometric configuration, and which can meet ordinary present day criteria for a full color video display. It would furthermore be desirable to provide a display technology which can be used to produce low cost, energy efficient, thin, flat panel, full-color video displays in conventionally rigid structures.
It is an insight, or understanding, of the present invention, that a limiting feature of known display technologies is the employment of electronically controlled pixel size light modulating elements in the display area. The light-modulating elements can, for example, be tricolor groups of light-emitting phosphors, in cathode ray or plasma displays, organic light-emitting diodes, tricolor groups of electrostatically shuttered filters, active matrix liquid crystal display elements and so on. A drawback of such displays is their reliance upon side-by-side RGB subpixels to achieve full color which limits the light output. The display intensity, or luminance of displayed primary colored images is limited by the need for an individual subpixel to illuminate the area of the group of three (or possibly four) subpixels, and manufacturing is complicated.
In many so-called “flat panel” display technologies, perhaps more clearly referenced as “thin panel”, or “thin, flat panel” display technologies, which avoid the bulk weight and energy-consuming drawbacks of cathode ray tube (“CRT”) devices, the light-modulating elements are synthesized in situ on a display panel substrate being a support structure for the eventual display. Such synthesis of electronically controllable optically active elements requires expensive techniques such as sputtering, vapor deposition, etching, and the like, may require exotic or exceptionally pure materials and the fabricated elements may be subject to contamination by ordinary structural materials such as common plastics materials that it would be desirable to use for substrates. In addition to the expense and manufacturing difficulties, the materials needed for synthesis of active devices, and the restraints on the substrate materials that can be used, may effectively impose requirements of rigidity on the end product display panel.
Furthermore, such known flat panel display technologies require x-y addressing of individual pixels employing extended conductor patterns and raising multiplexing issues resulting from the electrical cross-coupling of the rows and columns in the display medium. Various more or less complex drive schemes, can be used to inhibit cross-coupling, also known as “cross talk”. In addition to their cost, such measures may limit luminance, contrast or gray scale quality or the ability to refresh the display at video rates. As an alternative, an active matrix drive system can be used.
In a matrix display, driven by rows and columns, the pixels represent potential leakage paths from driven rows and columns to undriven rows and columns. Such leakage is the cause of cross talk. Some display media have a substantial threshold characteristic such that the signals that pass through to undriven rows and columns are below this threshold and do not affect the luminance and contrast. For display media with an insufficiently steep threshold, an active matrix can be used to provide a sharp threshold. This threshold sharpens the distinction between an “on” and an “off” pixel so that, for instance, a half-addressed pixel will not light, while a fully addressed pixel will. Cross-coupling in a display with an indistinct threshold can cause a display to partially illuminate when or where it is not intended to illuminate. However, if the threshold is sharp enough, small signals arising from cross coupling do not exceed the threshold and do not deleteriously affect display operation. An active matrix drive system, which usually incorporates one or more transistors at each pixel, provides a desired sharp threshold characteristic isolating the signal from the undriven rows and columns and avoiding activation of unaddressed pixels by spurious signals.
However, active matrix displays are relatively expensive. In addition, active matrix technologies, used in organic light-emitting diode (“OLED”) displays, and some liquid crystal displays (“LCD”), have other drawbacks. For example, fabrication of an active matrix display on a flexible substrate can be particularly difficult. Plastics are permeable to many impurities that can damage active elements or phosphors. Barrier layers needed for active matrices, even on glass, complicate manufacture and have been shown to delay damage rather than provide complete protection.
High yield, thin film transistor (“TFT”) fabrication on a glass substrate to yield a quality product having good dimensional stability requires substantial capital investment. Fabrication on a dimensionally variable plastic substrate, if successfully developed, would require even greater investment. Such processes typically require the substrate to be heated, creating difficulties with plastic substrates which may change their dimensions, deleteriously affecting the alignment of components in subsequent masking steps.
In the case of passive technologies for LCD, OLED or other displays the fabrication of long, narrow row or column electrodes from transparent conductive materials for example indium tin oxide (“ITO” herein), with sufficient current carrying capability for operation of a matrix display can be expected to present significant technical difficulties because of the limited conductivity of the transparent materials. Unavoidably high resistances in long conductors may cause line access times to be unduly high and cause excessive power consumption and heat generation.
Nor are passive matrix supertwist LCDs well suited to fabrication on or assembly with flexible plastic substrates because they require small and well controlled cell gap spacings. Other liquid crystal technologies, including ferroelectric, cholesteric and bistable nematic devices, being passive displays, require currents at video rates and power levels that are difficult to supply on flexible substrates with known transparent conductors.
Difficulties are expected in attempting to use phosphors, such as are employed in laser-based polymer flat panel displays and OLEDs, on a flexible plastic substrate, because phosphors require a protected environment to prevent degradation. CRTs use phosphors in a vacuum; plasma phosphors are contained in an inert gas at low pressure; and EL phosphors are sandwiched between insulating layers. These protected phosphor devices can have long lifetimes, whereas unprotected phosphors have rather short lives.
As taught, for example, in U.S. Pat. Nos. 4,336,536, 4,488,784, 5,231,559, 5,519,565, 5,638,084 and 6,057,814, the disclosures of which are hereby incorporated herein by reference thereto, over a period of several decades, inventor Kalt herein has developed electronically driven electropolymeric video displays that employ, as light shutter components of individual pixels, light-modulating capacitors having movable electrodes. The movable electrode is formed of metallized polymer film and is coiled, or otherwise prestressed, into a compacted, retracted position from which it can be advanced across a dielectric member by application of a drive voltage. The drive voltage is controlled by a fixed electrode on the other side of the dielectric member, the movable and fixed electrodes and the dielectric member constituting a variable capacitor.
Matrix arrays of such electropolymeric shutters are particularly suitable for use in electronic video displays because they can be fabricated from low-cost commercially available materials, consume little energy, are durable and are operable at video speeds. Of particular interest to a specific object of the present invention, electropolymeric shutter arrays, as taught by Kalt, can be embodied in flexible and shaped configurations.
Kalt '084 discloses a passive electropolymeric display (“EPD”) comprising a shutter array, constructed as just described, in front of a pixellated color screen having side-by-side red, green, blue and white cells aligned with the electropolymeric shutters. The display employs reflective color filters to be viewable by backlighting transmitted through the display and by reflected ambient light to have good visibility in both bright daylight and in subdued or dim interior light. This “indoor-outdoor” Kalt display is susceptible to low-cost web or sheet based manufacture, does not employ exotic materials or manufacturing processes, is low-weight and energy efficient and can be embodied in thin flat panels. Furthermore, they are compatible with flexible plastic substrates. In fact, the relatively high shrinkage coefficient of suitable synthetic polymeric plastics materials which would be problematic with other technologies is actually helpful to the fabrication of prestressed coiled shutter elements for electropolymeric shutter arrays. However, the light output of such electropolymeric displays is limited by the side-by-side subpixel configuration and a further drawback is the need for x-y addressing, or multiplexing of the shutter array.
In summary, there is a need for a for a low cost, low energy, video display capable of good luminosity or light output. Thin, flat panel, full color embodiments of such a display would be particularly desirable. There is also a need for flexible embodiments of such a display which can adopt different geometric forms, and there are still further needs for such displays that are capable of being manufactured from low cost materials and components by mass production methods.